1. Field of the Invention
This invention relates to a method, device, and video signal recording medium which is capable of performing a method that outputs a video signal having an additional information superimposed thereon, receives and extracts the received additional information, and performs duplication prevention control using the extracted additional information, for example, as in the case that a video signal recorded in a recording medium is played back, the video signal is transmitted together with an information for preventing duplication, the transmitted video signal is received, and recording on another recording medium is restricted or inhibited.
2. Description of Related Art
VTR (Video Tape recording devices) has been popularized in daily life, and many kinds of software which can be played back on a VTR are supplied abundantly. Digital VTR or DVD (Digital Video Disks) playback devices have been available commercially now, and provide images and sound of exceptionally high quality.
On the other hand, there is, however, a problem in that software applications of this great abundance can be copied without restriction, and several methods have already been proposed to inhibit duplication.
For example, though the method is a method which inhibits duplication of an analog video signal not directly, one method to prevent copying uses a difference in the AGC (Automatic Gain Control) system, or in the APC (Automatic Phase Control) system, for example, between the VTR recording device and a monitor receiver for displaying the image.
For example, the method which utilizes the difference in AGC system, in which a VTR performs AGC using a pseudo sync signal inserted in the video signal and a monitor receiver employs a different AGC system not using the pseudo sync signal, is an example of the former. In detail, when an analog video signal is recorded in an original recording medium, a very high level pseudo sync signal is previously inserted as a sync signal for AGC, and the very high level pseudo sync signal is inserted in the video signal to be supplied from a playback VTR to a recording VTR as a sync signal for AGC.
Alternately, the method which utilizes the difference of APC characteristics between a VTR and receiver as in the case that APC in a VTR can follow the color burst signal in a video signal with a short time constant but APC in a receiver follows with a relatively long time constant is an example of the latter. In detail, the phase of the color burst signal of a video signal is previously inverted partially when the analog video signal is recorded in an original recording medium, and the color burst signal having partially inverted phase is output as a video signal to be supplied from a playback VTR to a recording VTR.
As the result, the monitor receiver which receives the analog video signal from the playback VTR plays back the image correctly without being affected by the pseudo sync signal in AGC or without undesirable effects of the partial phase inversion of the color burst signal used for APC.
On the other hand, in a VTR, which is supplied with the analog video signal from the playback VTR into which pseudo sync signals have been inserted or which has been subjected to color burst signal phase inversion control as described herein above, for receiving such analog video signal and for recording the analog video signal in a recording medium, proper gain control or phase control based on the input signal cannot be performed, and so the video signal is not correctly recorded. Even if this signal is played back, therefore, normal picture and sound cannot be obtained.
As described herein above, in the case that involves an analog video signal, the method does not directly inhibit duplication but is a method for causing abnormally played back picture which can not be viewed normally. Such prevention method is a passive duplication prevention control.
On the other hand, in the case that a digitized information, for example, a video signal is involved, an anti-duplication signal or an anti-duplication control signal comprising, for example, a duplication ranking control code, is added as digital data to the video signal and recorded on the recording medium, so as to prevent or control duplication of the image.
FIG. 1 is a basic structural diagram of a duplication apparatus for duplicating digitized information, a digital information played back by the digital playback device 110 is sent to a digital recording device 120 through a digital transmission line 101, and the digital recording device 110 duplicates the digital information if duplication is permitted and does not duplicate the digital information if duplication is not permitted.
An anti-duplication control information in the form of additional information is recorded in a recording medium 111 placed on the digital playback device 110 in addition to a digital main information. The anti-duplication control information indicates control content such as duplication inhibition, duplication permission, or generation restriction. The digital playback section 112 reads out the information from the recording medium 111, acquires the anti-duplication control information together with the digital main information, and sends them to the digital recording device 120 through the digital transmission line 101.
An anti-duplication control signal detection section 122 of the digital recording device 120 detects the anti-duplication control signal out of the information received from the digital transmission line 101, and judges the control content The judgement result is sent to a digital recording section 121.
If the judgement result of the anti-duplication control signal from the anti-duplication control signal detection section 122 indicates permission of recording of the digital information input through the digital transmission line 101, then the digital recording section 121 converts the input digital signal to a digital information suitable for recording, and writes it in the recording medium 123, that is recording is performed. On the other hand, if the judgement result of the anti-duplication control signal from the anti-duplication control signal detection section 122 indicates duplication inhibition, then the digital recording section 121 does not perform recording processing of the input digital information.
Further, if the judgement result of the anti-duplication control signal from the anti-duplication control signal detection section 122 indicates permission of recording of only the first generation, then the digital recording section 121 converts the input digital signal to a digital information suitable for recording, and writes it in the recording medium 123, that is, recording is performed, and additionally, converts the anti-duplication control signal in the form of additional information to a signal for indicating duplication inhibition (duplication inhibition of next generation), and records it in the recording medium 123. Therefore, the video signal can not be duplicated further using the recording medium 123 in which the information is recorded.
As described herein above, in the case of a digital connection in which the main information signal and anti-duplication control signal added as an additional information are supplied to a recording device in the form of digital signal, because the anti-duplication control signal is contained in the digital data to be transmitted, duplication prevention control such as duplication inhibition is performed consistently in a recording device using the anti-duplication control signal.
In the case that the digital playback device in FIG. 1 is, for example, a digital VTR, in order to monitor the played back video signal and audio signal, both the video signal that is the main information signal, and the audio signal are converted to an analog signal through a D/A conversion circuit 113 and guided to an analog output terminal 114 connected usually to a monitor receiver.
As described herein above, though the playback device is a device for playing back digital signals, the anti-duplication control signal is not contained in the analog signal guided to the analog output terminal 114. Therefore, in the case of an analog connection in which an analog device such as analog VTR is connected to the analog output terminal 114, duplication of the information signal is undesirably possible.
Though it is considered that the anti-duplication control signal is superimposed and added on the D/A converted video signal and audio signal, it is difficult for the anti-duplication control signal to be added, extracted in a recording device, and used in duplication prevention control without deterioration of the D/A converted video signal and audio signal.
Therefore, heretofore in the case of analog connections only the passive duplication prevention method utilizing the difference in AGC system or the difference in APC characteristic between a VTR and monitor receiver described herein above has been an available duplication prevention control method.
However, in the case of the duplication prevention control method utilizing the difference in AGC system or APC characteristics between a VTR and monitor receiver described herein above, it can happen to record the video signal normally and to fail in even the passive duplication prevention dependently on the AGC system or APC characteristics of the recording device side. Further, it can happen to cause disturbance of played back picture on the monitor receiver. These are problems in duplication prevention control.
The inventors of the present invention has proposed previously a method in which a anti-duplication control signal is spectrally spread, the spectrally spread anti-duplication control signal is superimposed on the analog video signal, and the video signal is recorded in the form of digital record or analog record (refer to U.S. patent application Ser. No. 08/75510) as a duplication prevention control method which can solve the problem described herein above and is effective for both analog connection and digital connection without deterioration of the played back picture and sound.
According to this method, a PN (Pseudorandom Noise sequence code (referred to hereinafter as PN code) used as spread code is generated at a sufficiently fast rate and spectrally spread by multiplying it by the anti-duplication control signal. In this way, a narrow-band high-level anti-duplication control signal is converted to a wide-band low-level signal which does not affect adversely the video signal or sound signal. This spectrally spread anti-duplication control signal is then superimposed on the analog video signal, and recorded in a recording medium. In this case, the signal to be recorded in a recording medium may be an analog signal or a digital signal.
In this method, because the anti-duplication control signal is spectrally spread and superimposed on the video signal as a wide-band low-level signal, it is therefore difficult for a person who wishes to illegally duplicate the video signal to remove the anti-duplication control signal which is superimposed on it.
However, it is possible to detect and use the superimposed anti-duplication control signal by performing inversion spectral spread. This anti-duplication control signal is therefore supplied to the recording device together with the video signal. In the recording side, the anti-duplication control signal is detected, and duplication is consistently controlled according to the detected anti-duplication control signal.
However, in the case of a system in which an anti-duplication control signal is spectrally spread and it is superimposed on the video signal, in some cases, the spectrally spread anti-duplication control signal is removed, deteriorated or changed by using the noise removal system for video signals
For example, in the case of the noise removal system for removing noise in a video signal by utilizing correlation between picture elements of video signals, between frame intervals, or between fields, the difference is taken between adjacent video signals of adjacent horizontal scanning lines, adjacent fields or adjacent frames, and the difference obtained is removed as noise.
In this case, it can happen that the anti-duplication control signal spectrally spread and superimposed on the video signal is calculated as the difference, and it is removed as mentioned above. And when it is removed, it can happen that the spectrally spread anti-duplication signal is changed to a different spectrally spread anti-duplication control signal.
Further, when the noise removal system mentioned above is used, though not all anti-duplication control signals spectrally spread and superimposed on the video signal, are removed it can happen that an anti-duplication control signal superimposed on the video signal is removed partially, and an anti-duplication control signal deteriorates. In this case, a correct anti-duplication control signal superimposed on the video signal cannot be extracted, and the playback prevention control corresponding to an anti-duplication control signal is not performed.
Further, for example, in the case that a so-called horizontally-long wide television image of 16:9 aspect ratio is converted into a television image of standard 4:3 aspect ratio, or in the case that a television image is converted conversely, when picture element data are thinned out or interpolated in the horizontal direction, or a picture is enlarged or reduced in right and left direction, the anti-duplication control signal spectrally spread and superimposed on the thinned out video signal disappears, or the spectrally spread anti-duplication control signal using the interpolated data becomes discontinuous, and then it can happen that an anti-duplication control signal is impossible to be restored to the original state by spectrum reverse diffusion.
Further in the case that NTSC system is converted into PAL system, or in the case of inverse conversion, when, system conversion between different television systems having different number of scanning lines is performed, the same problem as described above can happen in this case during performing thinning out and interpolation processing in horizontal line unit.
Because the video signal of 1 field is composed again using the video signal of several fields when special speed playback such as slow playback or double speed playback is performed on a VTR, in this video signal composed again, it can happen that the spectrally spread anti-duplication control signal becomes discontinuous, and an anti-duplication control signal cannot be restored to the original state by inversion spectral spread.
In the case that so-called cut editing is performed and video signal in field unit is thinned out, in video signal after cut editing, the spectrally spread anti-duplication control signal becomes discontinuous similarly, and the anti-duplication control signal becomes impossible to be restored to the original state by way of inversion spectral spread.
The conventional spectral spread can involve only small quantity of information to be superimposed on as the additional information such as anti-duplication control signal, it is also a problem.
In view of the above-mentioned problems, it is the object of the present invention to provide a method, device, and video signal recording medium in which the above problems are eliminated, and additional information spectrally spread superimposed on the video signal is transmitted consistently to the receiver, the complete additional information can be extracted, and the quantity of additional information to be superimposed is increased.